The aqueous humor of the eye is thought to be secreted by the epithelium of the ciliary body. This epithelium has been difficult to study, in part because of its complicated morphology. The authors attempted to circumvent this difficulty by growing the epithelial cells in tissue culture. A procedure is described for producing pure primary cultures of rabbit nonpigmented ciliary body epithelial cells. This procedure was used with whole-cell patch-clamp recording to characterize voltage-activated currents in the nonpigmented cells. These experiments show that most nonpigmented cells contain two kinds of currents: a rapidly activating and inactivating inward current, carried by Na+ and blocked by tetrodotoxin (TTX), and a more slowly activating and inactivating outward current, blocked by tetraethylammonium (TEA+), Ba2+, and 4-aminopyridine (4-AP) and presumably carried by K+. Both of these currents have been observed in freshly dissociated cells and in cultures up to 7 days old. The voltage-gated currents in ciliary body epithelial cells are remarkably similar to those of neurons and raise the possibility that these epithelial cells are capable of spike propagation.